ESP8266 Tx drive current of only 70micro amps

[kevinateev]

Hi Ya'll, so I'm getting deeper into this stuff of the new age, ESP8266.  Where I've used NodeMcu just fine in the past, I now have the ESP8266Mod on it's own.

When I power it up, on the scope and with the logic analyzer, I see the startup message. ... mode (1,7) ... However, when I hook it up to optio-isolated USB adapter, there is no signal.  I've configured the adapter in loop-bcack (connect TX and RX on optio side) and I get echo as expected on computer.

So, after checking numerous times, I refer to specs. the Tx should have up to 12ma drive current.  So, I hook up a 10Kohm resistor to the normaly high output.  It drops to 0.7 Volts.  That looks like only 70 micro-amps of current output.  Hmm, it should easily be 330 micro-amps of output and virtually no voltage drop with that kind of load.

What you think?  Unit appears to be functioning but drive transistors are fried for this GPOI pin?

[Doctorandus_P]

I am not too deeply involved in particular ESP8266 architecture, but it's very common for uC's to have configurable I/O. If it's from a self written program, it may be an error in a register setting. For example instead of switching an output to high and low, you're turning an internal pullup resistor on and off.

It is also quite common to damage single I/O pins by overload, or ESD damage from touching them, or over currents from accidental connection to a (too high or low (negative)) voltage rails.

When electronic hardware fails, there is no way in predicting in which way it fails. I once had an AVR with a faulty ADC pin. The ADC worked normally on all other pis, and the damaged pin also worked normally with digital I/O. Only the analog part of that single pin was damaged.

The easiest way to distinguish between firmware and hardware errors is to take another ESP8266 and program it with the same firmware. If the new one functions normally, then a damaged I/O pin is the most likely cause. If they bot act the same, then Firmware is much more likely, or you have faulty external hardware that blows up pins of your uC. I once had 5 damaged uSD cards before I narrowed it down to a faulty card reader.

The surest solution is to just throw it away, and for the price of an ESP8266 it's not much of a loss (You do buy them in packs of ten I hope?)
Re using such damaged hardware can be tempting.  If you do not want to throw away a whole PCB because of a single damaged pin, then at least break that pin off the board. This will save you some headaches if you re-use that PCB for another (temporary) project in half a year time.

[kevinateev]

It is fun when stuff works but it is also kind of facinating when it fails.

This part is from a salvaged NodeMcu unit that I did fry somehow.  I'm out of parts and more are on order!  So, in fooling around, I put it on a scope and was surprised to see the boot message, then I'd hooked it up to UART-USB adapter and ... nothing.  Odd, that is what lead me down this road .. free COVID time ultimately.  Yes, cheap part not worth the trouble.  Shipping time is forever however.

So, hooked up a 2N3604 and had some success with that but still not good enough, needs source/sink circuitry so gave up on discrete transistors and used a pair of Schmitt triggers and it works! (part SN74HC14N).

But really, this part is destined for garbage once new onces come in ... may get me by with testing though.

Thanks for sharing!